In coal mines where the coal exists in the form of relatively thin layers or seams it has long been the practice to employ coal-handling equipment which has a sufficiently low profile or height to be accommodated in the low-clearance areas formed as the coal is mined. One widely used mining technique includes the use of so-called feeder-crusher machines which rerecive freshly mined coal from a mining machine or haulage vehicle, crush the coal to a smaller more manageable size and feed it to a conveying system for removal from the mine.
Current feeder-crushers are mobile low-profile machines having a horizontally elongated hopper-like body fitted intermediate its ends with a rotary crusher. Horizontal transverse flights carried by a pair of endless chains continuously move along the floor of the body and in so doing they urge coal from the receiving end of the body to the rotary crusher and move the resulting crushed coal away from the crusher toward the rear end of the body where it is discharged. The discharged coal falls on to an endless conveyor which may be one of a series leading out of the mine. A typical feeder-crusher will not exceed about four feet in height in order that it can be maneuvered into a low-clearance space.
The body and the rotary crusher are interconnected with rigid frame members to form a unitary structure which supports the components of the power system required for operation of the machine. Typically, the entire structure is supported on a crawler-type propelling unit operated by a hydraulic or in some cases electric motor. Typically the power system includes an electric motor and a hydraulic pump driven by the motor. Electric current is supplied to the motor by cables leading into the mine. The pump supplies pressurized hydraulic fluid for operating the crawler unit and for operating a separate hydraulic motor which drives a speed reduction unit having its output connected to the rotary crusher shaft.
The rotary crusher is typically of the hammer mill or impact type in which a horizontal rotating shaft is provided along its length with a plurality of radial striker arms or hammers. The shaft is disposed transversely of the body of the machine, and as the coal is urged into the hammer circle between the shaft and the floor of the machine, by means of the moving flights, it is struck and crushed by the striker arms. The coal passes through the hammer circle only once, so that the arms are continually acting on fresh coal.
Since all of the material received by a feeder-crusher passes through the crushing assembly, the crushing of the coal must be carried out continuously and at a high rate if the machine is to operate effectively. The crusher is the limiting feature of the machine, because the conveyor system can be constructed to handle essentially any input load. Therefore, any increase in the ability of the crusher to handle a greater throughput increases the capacity of the machine. In addition it is important to reduce down-time due to jamming of the crusher or breakage of any part of the crusher drive system. Inherently the coal will include rock in varying amounts and the rock being harder and more resistant to crushing will sometimes tend to wedge between the floor of the machine and the breaker arms or will create very high strains in the drive system. The result can be jamming of the crusher and/or shearing of a shear pin which is typically inserted between the crusher shaft and the output shaft of the drive system. The machine is then out of operation until the fault has been remedied, and during this time loading of coal into the receiving end of the machine must stop, thereby reducing production.
The solution of the problems relating to increasing the throughput of a crusher system in a feeder-crusher and to reducing down-time resulting from jamming or breakage do not lie merely in increasing the size and power of the crusher system. The principal reason for this is that it is not practical or economical to install heavier and larger drive components and/or heavier and larger crusher shafts. As previously noted the height of the machine must be limited to about four feet; current construction techniques and the power requirements of the machines result in essentially all useable space being occupied. Further, the length, width and weight of the machines are limited as a result of the limited space in which the machines must operate.